Conventionally, assuming the advancing direction of an electron as a Z axis, it is necessary for a spin rotator to include two kinds of mechanisms consisting of a mechanism which rotates the electron in a plane including the Z axis and a mechanism which rotates the electron in a XY plane perpendicular to the plane including the Z axis. With respect to the latter mechanism, although there may be a case where a mechanism which mechanically rotates a sample or a detector is provided, as a method which rotates an electron electromagnetically, a method which uses an axis-symmetric magnetic field lens proposed by Duden et al. and is disclosed in non-patent literature 1 has been used most popularly.
Hereinafter, the method is explained in detail in conjunction with explanatory views of the prior art shown in FIG. 12 to FIG. 16.
FIG. 12 is a view which is prepared by writing a magnetic potential distribution in a cross-sectional view of such a spin rotator, wherein a trajectory of an electron beam incident on the spin rotator is shown together with condenser lens systems (CL2, CL3) arranged behind the spin rotator.
As a spin rotator which rotates an electron beam in a plane which includes a Z axis, there has been known a device as disclosed in a paper written by Duden et al. introduced previously where a 90° electric field deflector and a 90° magnetic deflector overlap with each other. FIG. 13(a) shows a 90° deflection-type spin rotation mechanism constructed based on the substantially same principle as the spin rotator shown in FIG. 12 together with round lens systems arranged in front of and behind the spin rotation mechanism. When the direction of spin is equal to the advancing direction of an electron, by performing the 90° deflection using only an electric field, as shown in FIG. 13(b), the advancing direction of an electron is rotated by 90° although the direction of spin of a discharged beam is not changed and hence, the direction of spin has the inclination of 90° with respect to the advancing direction of an electron. When the 90° deflection of the electron beam is performed using only a magnetic field, the spin is rotated along with the rotation of an electron as shown in FIG. 13(c) and hence, the direction of spin is equal to the advancing direction of the electron even after the 90° deflection. By realizing the 90° rotation by simultaneously applying an electric field and a magnetic field to the electron beam, the direction of spin can take an intermediate value between 0° and 90°.
In the case of the device of the above-mentioned type, it is always necessary to rotate an electron beam by 90°. Depending on the device, however, there is a case where this rotation by 90° is not so desirable. That is, there is a case where it is desirable to rotate only the spin while keeping the advancing direction of an electron straight. To satisfy such a request, there has been known a method which uses a Wien filter as disclosed in non-patent literature 2.
FIG. 14 shows one example of a spin rotator of a Wien filter type where the spin rotator is sandwiched between round lenses. FIG. 14 also shows a case where the simulation of a trajectory of an electron is performed in a state where an electric field and a magnetic field of the Wien filter are turned off and a case where the simulation of a trajectory of an electron is performed under a condition that spin is rotated by 90°.
The Wien filter adopts the same principle as a spin rotator of a 90° deflection type and hence, an electric field and a magnetic field are applied to an electron beam in an overlapping manner in the same manner as the spin rotator of a 90° deflection type. However, the Wien filter differs from the spin rotator of 90° deflection type with respect to a point that the direction of a voltage and the direction of a current are set such that the direction of deflection of an electron generated by an electric field and the direction of deflection of the electron generated by a magnetic field become opposite to each other. In the spin rotator of 90° deflection type, the direction of a voltage and the direction of a current are set such that the direction of the deflection of an electron generated by an electric field and the direction of the deflection of the electron generated by a magnetic field become the same.
In the Wien filter, the direction of deflection of an electron beam generated by an electric field and the direction of deflection of the electron beam generated by a magnetic field become opposite to each other and, at the same time, the magnitude of the electric field and the magnitude of the magnetic field are set such that the magnitude of deflection generated by the electric field and the magnitude of deflection generated by the magnetic field are always the same so that an electron beam advances straightly as a result. This condition for making an electron beam advance straightly is referred to as the Wien condition and the Wien condition is expressed by E1=vB1. E1, B1 and v are the magnitude of a uniform electric field, the magnitude of a uniform magnetic field and the velocity of an electron respectively. The spin is rotated only by the magnetic field and the magnitude of the rotation is expressed as follows.Frequency of Larmor precession: ω=eB/m Rotational angle: α=Lω/v=LeB1/mv L: length of filter
Here, to substitute the Wien condition E1=vB1 and the square of velocity v2=3eUo/m into α=Lω/v=LeB1/mv, the rotational angle α is expressed by a formula α=LE1/2Uo.
To convert a value E1 of an electric field into an electric pole voltage V1 which generates the value E1 of an electric field, the electric pole voltage V1 is expressed by the following formula.V1=E1R
R: radius of round hole at the center,
Assuming α=π/2(90°), Uo=20,000V, R=5 mm, L=80 mm, the electric pole voltage V1 is obtained as follows.V1=2×20,000×5π/2×80=3926.69V
A magnetic field is obtained based on the Wien condition described previously.
When the Wien filter is used, it is necessary to bring the magnitude of an electric field and the magnitude of a magnetic field into the relationship which always satisfies the Wien condition for making an electron beam advance straightly. Accordingly, to adjust the electron beam at various spin rotational angles, the technique that a spin rotational angle is set to a fixed value by combining an electric field and a magnetic field as in the case of the 90° deflector is not adopted. That is, a spin rotational angle is determined by adjusting a value of a magnetic field. In view of the above, as shown in FIG. 14, a lens condition on a preceding stage of the Wien filter is set such that an electron beam is focused on the center of the Wien filter. Due to such setting of the lens condition, as shown in the drawing on a lower side of FIG. 13, even after a case where spin is rotated by applying an electric field and a magnetic field to an electron beam, a lens condition on a succeeding stage of the Wien filter does not largely deviate and hence, the readjustment of a condenser lens system can be minimized and it is possible to rotate only the spin.    Non-patent Literature 1: T. Duden, E. Bauer, A compact electron-sipin-polarization manipulater, Rev. Sci. Instrum 66(4) 1995, 2861-2864    Non-patent Literature 2: T. Kohashi, M. Konoto, K. Kike J-Electorn Microscopy 59(1)(2010)43-52.    Non-patent Literature 3: T. T. tang, Optik 74 (1986) 51-56.